Abstract:

Aim: Ex situ conservation is an important complement to in situ conservation, yet current ex situ practices often pay insufficient attention to maintaining genetic representativeness and integrity, limiting the long-term persistence and authenticity of ex situ populations. We investigated the genetic lineages and demographic history of the Chinese endemic Tertiary relict tree Parrotia subaequalis and developed an integrated framework for its ex situ conservation. 

Methods: We integrated field resource surveys, whole-genome resequencing, community phylogenetic analyses, ecological niche modeling, and artificial propagation experiments to characterize genetic diversity and evolutionary history, identify suitable habitats and companion species for ex situ conservation, and optimize propagation protocols. 

Results: Population genomic analyses identified four distinct genetic lineages (AD). Phylogenetic and genetic composition analyses revealed that the contemporary center of genetic diversity in P. subaequalis is located in the eastern mountainous region spanning the Zhejiang-Anhui border (from the Tianmu Mountains to the Tiantai Mountains), where all four genetic lineages are represented. In contrast, populations in the western Dabie Mountains consist exclusively of the genetically homogeneous lineage A, with individual genotypes showing signatures of recent differentiation. This distribution pattern is consistent with the founder effect associated with the postglacial westward expansion of P. subaequalis from eastern microrefugia. Ecological niche modeling further supported a Holocene range expansion of lineage A from east to west. Demographic reconstruction revealed a continuous decline in effective population size across all lineages since approximately 0.3 million years ago (Ma), indicating that glacial isolation in microrefugia followed by postglacial dispersal jointly shaped the contemporary genetic structure of the species. Community phylogenetic analyses identified environmental filtering as the dominant mechanism of community assembly, with the strongest filtering occurring between 400 and 800 m elevation. Based on these results, we identified 19 suitable companion species to guide ex situ site selection and community design. Ex situ cultivation trials further demonstrated that this elevational range provided the most suitable conditions for seedling growth, with maximum stem diameter and seedling height recorded at 565 and 835 m, respectively. Orthogonal experiments optimized containerized seedling production, resulting in the propagation of 11,436 container-grown seedlings and the establishment of two ex situ conservation populations representing all four genetic lineages. 

Conclusion: By integrating genetic structure analyses, community assembly, artificial propagation, and long-term monitoring, we established a comprehensive ex situ conservation system for P. subaequalis. This integrated framework preserves genetic diversity and evolutionary potential while facilitating sustainable population establishment, and provides a transferable model for the conservation of other relict and threatened woody plants.

Key words: Parrotia subaequalis, ex situ conservation, whole-genome resequencing, genetic lineage, community phylogeny, Tertiary relict plant